Underground storage system



L. P. MEADE UNDERGROUND STORAGE SYSTEM Feb. 5, 1957 5 Sheets-Sheet 1.

Filed April 27, 1953 INVENTOR. 1;. B W

WM w M ATTORNEYS 3 Sheets-Sheet 2 Feb. 5, 1957 L. P. MEADE UNDERGROUND STORAGE SYSTEM Filed April 27. 1953 w R 4, m 6 4/ m 6 X l \WX fl m M d a Q N P 3 WW I z: o I|| I 1 v I i l HUIHI 0 w 7 9 a W I l 1 i L 8 6 0 g k w y H w w A r 4 w w n wf' 'v A TTO/PNEYS Feb. 5, 195'? L. P. MEADE 2,780,070

UNDERGROUND STORAGE SYSTEM Filed April 27. 1953 3 Sheets-Sheet 5 INVENTOR. By L BMeade m4 *1 United States Patent UNDERGROUND STORAGE SYSTEM Leonard P. Meade, Bartlesville, Okla, assignor to Phillips Petroleum Company, a corporation of Delaware Application April 27, 1953, Serial No. 351,297

11 Claims. (Cl. 62-1) This invention relates to underground storage systems. In one of its more specific aspects, this invention relates to a means for withdrawing fluid stored in an underground storage system. In another of its more specific aspects, this invention relates to a rotary hydraulic motor and pump and its use in an underground storage system.

A definite problem in providing storage facilities for liquefied petroleum gas has been created by the constantly expanding production and seasonal use of this material. Because of the high vapor pressure of liquefied petroleum gas, particularly propane, the cost of storage in surface equipment, such as steel tanks, becomes excessive due to the massive construction required to withstand the vapor pressure of the stored material in a safe manner. Where it is necessary to store large quantities of such materials during the off season, this problem becomes extremely acute. In addition to the expense involved, the use of steel tanks is limited by shortages in production. In order to overcome these difiiculties it has been proposed to store liquefied petroleum gas in porous water-bearing formations, in water-leached caverns in salt formations, or in abandoned mines in impermeable shale or limestone formations. Further, underground concrete storage tanks and buried sections of pipe have been used to a limited extent in the storage of liqufied petroleum gas.

In accordance with this invention, an underground storage system for liquefied petroleum gas is provided which is capable of storing extremely large quantities of this material at a very small cost. Further, a number of operating and safety features are provided to ensure a long period of trouble-free operation of the storage system and to get easy and reliable introduction of the material into storage and removal of the material therefrom. In particular, this invention provides an improved means for Withdrawing the fluid from the underground storage system.

The following objects will be attained by the various aspects of the invention.

It is an object of the invention to provide underground storage facilities of novel construction and arrangement, said facilities providing storage at a minimum unit cost.

It is a further object to provide a system in which the material can be easily introduced into the system and removed therefrom.

It is a further object to provide a hydraulic pumping system whereby the material in storage can be readily removed.

It is a still further object to provide an underground storage system capable of storing materials, such as propane, having a high vapor pressure for an extended period with a minimum of operating difficulties.

Various other objects, advantages and features of the invention will become apparent from the following detailed description taken in conjunction with the accompanying drawing, in which:

Figure l is a vertical sectional View, partially in elevation, of the underground storage system of this invention;

of Figure 3;

Figure 5 is a sectional view taken along the line 5--5 of Figure 3;

Figure 6 is a sectional view taken along the line 6-6 of Figure 3; and

Figure 7 is a sectional view taken along the line 7--7 of Figure 3.

Referring to the drawing in detail, and particularly to Figure 1, the underground storage system of this invention includes one or more underground storage caverns, one of which is indicated by reference numeral 10. It will be understood that each cavern can consist of a large excavated region, as illustrated in Figure 1, or, alternatively, the cavern can comprise a series of elongated individual storage chambers of cylindrical or rectangular cross section with the axis of the storage chambers in a horizontal or vertical direction, as desired, all of the chambers defined in the cavern communicating with a common tunnel leading to a central shaft in the manner hereinafter explained.

A tunnel 11 connects the cavern 10 with an enlarged shaft 13 extending to the surface. A drilled hole 12 extends from shaft 13 to the upper region of cavern 10 and provides means for equalizing the vapor pressure within cavern 10 and shaft 13. The bottom region of the shaft preferably extends a short distance below the floor of the tunnel, thereby defining a recess or well 14. It will be understood that, where a plurality of caverns are utilized, each cavern can be connected to the central shaft by a separate, preferably horizontal, tunnel. The shaft 13 is usually vertical but, where the cavern is formed in the side of a mountain or cliff, the shaft can be inclined, or even horizontal.

The cavern 10 is advantageously formed in an impermeable rock formation, such as a limestone formation. This limestone formation is indicated by numeral 16 and extends a short distance above the top of the cavern so that the material in storage is effectively sealed by the limestone formation. Each cavern 10 is provided with a drilled 'hole 17 extending from the surface of the earth to the top of the associated cavern. Positioned within the drilled hole is a filler line 18 and a vent line 19 whereby material can be introduced into cavern 11 or vapors can be removed therefrom. Filler line 18 is connected through line 20 to a source of supply as a pipe line, storage tank, etc.

Stored material is removed from the cavern by pump assembly 21 positioned within shaft 13. This assembly includes casing string 22 supported by casing head 23 and extending downwardly through well head 24, tubular metal liner 26, and the lower portion of shaft 13 into Well 14 formed at the bottom of the shaft. Liner 26 provided at the top of the shaft is anchored by a mass of material 27 such as cement disposed about the exterior of the liner. The liner extends a substantial distance downward in the shaft, and serves to prevent the flow of liquids into the shaft and to support the walls of the shaft. At the bottom of well 14, casing string 22 is received within enlarged section of pipe 28 which is anchored in a mass of material such as cement at the bottom of the well. The casing string includes a valve 29 just above well head 24. Disposed at the lower end of casing string 22 is a valve 31, and immediately above this valve rotary pump 32 and motor 33 are supported by tubing string 34 disposed concentrically within casing string 22. Tubing string 36 is disposed concentrically within tubing string 34, and is connected to the inlet of rotary hydraulic motor 33. Tubing string 34 with its concentric tubing string 36 extends through pipe 37 and valve 38 to a combination tubing head and slip joint 39. Secured to combination tubinghead and slip joint 39 is a pipe 41 communicating with the interior of tubing string 34 and provided with an outlet conduit 42. Immediately above outlet conduit 4-2 is a sealing member 43 through which extends tubing string 36. Fluid feed line 44 connected to the outletof pump 46 supplies fluid to tubing string 36 which, being connected to the inlet of rotary hydraulic motor 33, supplies power fluid to this motor. Feed line 47 connected to line 48 leading from outlet conduit 42 supplies fluid to the inlet of pump 46 through line 49. Line 51, which may be connected to a pipe line, storage tank, etc., is also connected to line 4-9 for the purpose of supplying fluid to pump 46. Valves 2, 53 and 54 are provided in lines 47 and 51 to control the fluid flowing to pump 46.

In assembling pump assembly 21, valve 29 is opened, and easing string 22 is hung from casing head 23 so that it extends downwardly through valve 29 to its position within pipe 28. Valve 31 is normally closed so that after the casing string is inserted and the casing head sealed, no material can pass through the casing to the surface nor between the casing and the casing head body. Tubing strings 34 and 36 are next lowered into the well section by section, rotary hydraulic motor 33 being secured to the lowermost section of tubing string 34 and the lowermost section of tubing string 36 being connected to the inlet of said motor. Rotary hydraulic pump 32 is operatively connected to motor 33 land is lowered with the motor. When pump 32 is disposed a short distance above valve 31, the interior of the casing is pressurized by connecting valves 56 and 57 so that the pressure in the casing is equalized with the pressure in the underground storage system. Combination tubing head and slip joint 39 is so constructed that the space between the casing and tubing string 34 is completely sealed when the pump is so disposed. Tubing strings 34 land 36 are thereafter lowered to their final position, thereby causing pump 32 to engage valve 31 so as to open it. Combination tubing head and slip joint 39 is so constructed that the vapor in the casing cannot escape when the tubing string, motor and pump are lowered to their final operating positions. Sealing member 43 prevents escape of vapor through the space between tubing strings 34 and 36. In addition, valves may be provided in lines 44 and 48 to prevent leakage from tubing strings 34 and 36, respectively.

When it becomes necessary to remove the pump, tubing string 34 is raised a sort distance so that pump 32 moves out of engagement with valve 31 allowing the valve to close, thus sealing the lower end of the case. Any fluid pressure existing in the casing can then be removed by venting the interior of the casing to the atmosphere. During the raising of tubing string 34 to close valve 31, the interspace between the tubing and the casing, because of the construction of combination tubing head and slip joint 39, remains sealed. Pipe 37 is provided with a pressure gauge assembly 58 and a valved pipe 57, the described venting being effected by connecting a conduit from pipe 57 to a vent pipe. After the pressure has been vented, sections of tubing strings 34 and 36 can be readily lifted and removed with resultant lifting of rotary hydraulic pump 32 and motor 33 out of the shaft. When the removal is completed, valve 38 can be closed to provide a positive seal implementing the seal produced by valve 31. 7

"Referring to Figure 2 and Figure 3, which is a sectiona'l view taken along the line 33 of Figure 2, of the drawing, there'is illustrated a rotary hydraulic motor 33 and pump 32. A cylindrical casing 66 is separated into an upper chamber 67 and alower chamber 68 by a cross men-wa m An adapter '71 is threaded into the top of casing 66 and serves as a closure member for chamber 67. Adapter 71 has a fluid inlet passageway 72 therethrough which communicates with the interior of chamber 67 near its periphery. The upstream end of passageway 72, located substantially in the center of adapter 71, is threaded so that it can be readily connected to tubing string 36. Adapter 71 also has a fluid outlet passageway 73 therethrough which communicates the interior of tub ing string 34 with chamber 67 near its periphery. The upstream end of passageway 73 is located substantially diametrically opposite to the downstream end of passageway 72. lassag'eway 74 which extends through cross member 69, and connects chamber 67 with chamber 68 is located near the peripheries of chambers 67 and 68 and substantially directly below passageway 73. A second adapter 76 is threaded into the bottom of casing 66 and serves as a closure member for chamber 68. Adapter '76 has a fluid inlet passageway 77 therethrough which communicates the interior of chamber 68 with the interior of strainer 78 which is attached to the lower part of adapter 76 and through which the fluid to be pumped asses. The downstream end of inlet passageway 77 is positioned substantially directly below the downstream end of inlet passageway 72 and near the periphery of chamber 68. Slotted rotor 79 is eccentrically positioned within chamber 67 and has an upper shaft 81 which rides in bearing 82 formed in adapter 71 and a lower slraft 83 which rides in bearing 85 formed in cross member 69. Slotted rotor 84 is eccentrically positioned within chamber 68, and has an upper shaft 86 which rides in bearing 85 and a lower shaft 87 which rides in bearing 88 formed in adapter 76. All of the bearings are self-lubricating and may be lined with nylon or Teflon. Lower shaft 83 of rotor 79 and upper shaft 86 of rotor 84 are rigidly connected to one another as by a spline coupling. Impeller vanes '89 ride in the slots of rotors 79 and 84 and are maintained in contact with the walls of chambers 67 and 68 by springs. The cut-away portion of rotor 67 in Figure 2 shows springs 91 in both compressed and expanded positions.

Figures 4, 5, 6 and 7 are sectional views taken along the lines 44, 5-5, 66 and 7-7 of Figure 3, and illustrate the positions of rotors 79 and 84 within chambers 67 and 68. Impeller vanes 89 are in contact with the walls of the chambers, and the direction or rotation of the rotor is as indicated in the figures. The figures show also the positions and approximate shapes of the ends of the fluid passageways as follows: in Figure 4, the downstream end 96 of fiuid inlet passageway 72 and the upstream end 97 of fluid outlet passageway 73; in Figure 5, the downstream end 98 of fluid passageway 74; in Figure 6, the upstream end 99 of fluid passageway 74; and in Figure 7, the downstream end 101 of fluid inlet passageway 77. The ends of the fluid passageways are shown as occupying an arc of slightly less than and while they may take other shapes, for most eflicient operation, they should take the form indicated. Four (4) impeller vanes 89 ride in slots in each of the rotors, and are spaced at 90 intervals. It is not, however, intended to limit this invention to the use of four such vanes, but if the number of vanes are varied, it may be necessary to change the are occupied by the ends of the fluid -passageways. In any event for efficient operation, the two portions of the chambers not open to the fluid passageways should each define an arc greater than the angle between the vanes. Thus in Figure 4, the two arcs defined by points 102 and 1tl3 and points 104 and 106 should be greater than the angle between vanes 89.

In the operation of the rotary hydraulic pump and motor, referring to Figures 2 and 3, power fluid enters fluid inlet passageway 72 from tubing string 36 and occopies the space between two of the impeller vanes 89. When this space becomes completely filled with fluid, the introduction of additional fluid causes rotor 79 to rotate, carrying with it the fluid entrapped between th two impeller vanes. Fluid now entering through passageway 72 will cause succeeding spaces formed by the impeller vanes to be filled, thus continuing the rotation of rotor 79. With the continued rotation of rotor 79, the fluid originally entrapped is discharged-through passageway 73. As illustrated in Figure 4, power fluid is entering chamber 67 through end 96 of passageway 72, and is being discharged through end 97 of passageway 73.

Since the two rotors are rigidly connected, the rotation of rotor 79 causes rotor 84 to rotate as well. The fluid which it is desired to pump enters passageway 77 through strainer 78 and is entrapped between the impeller vanes 89 riding in slots of rotor 84. Continued rotation of rotor 84 carries the entrapped fluid around to the point at which it is discharged through passageway 74 into the stream of power fluid being discharged from chamber 67 through passageway 73. As illustrated in Figures 6 and 7, fluid is entering chamber 68 through end 101 of passageway 77 and is being discharged through end 99 of passageway 74. Referring to Figures 4 and 5, the fluid leaves passageway 74 through end 98 of passageway 74 and enters end 97 of passageway 73. In operation the power fluid supplied the motor must be of the same composition as the fluid to be pumped. Thus, it is apparent that the power fluid discharged from the motor and the fluid discharged by the pump leave the,

motor-pump assembly through the same passageway 73 and thereupon enter tubing string 34. In the overall operation of the storage system, referring to Figure 1, a fluid, such as propane, is introduced into cavern 10 through filler pipe 18. Filler pipe 18 is supplied by line 20 which may lead to a pipeline, storage tank, etc. It is to be understood that a plurality of caverns may be provided with filler pipes, as desired.

When it is desired to remove stored material from cavern 11, valves 29 and 38 are open, and fluid of the same composition as the stored material is supplied rotary pump 46 through lines 51 and 49. As shown, this fluid may come from the same source which originally supplied cavern 10. Rotary pump 46 discharges power fluid through line 44 which is connected to tubing string 36. Power fluid entering tubing string 36 is supplied to motor 33 which rotates pump 32. The pump picks up fluid at the lower end of casing string 22 and discharges same through the fluid outlet passageway of the motor along with the power fluid discharged by the motor into tubing string 34. The fluid being pumped and the power fluid rise to the surface through tubing string 34, and leave the tubing through discharge conduit 42. Line 48 is connected to discharge conduit 42 and may lead to a storage tank, pipe line, etc. After pump 46 has been started initially, its fluid supply may be taken from the discharge of the motor-pump assembly through line 47.

When operating in this manner valves 52 and 53 would be open while valve 54 would be closed.

It is evident that I have provided an underground storage system whereby the material to be stored can be easily introduced in the system and thereafter readily removed.

The rotary hydraulic motor and pump because of its construction provides a compact, rugged unit which can be readily inserted and withdrawn from the shaft. Furthermore, by providing a hydraulic pumping system, a positive, elficient and safe means is made available for removing fluids from underground storage.

Although Ihave described my invention with a certain degree of particularity, it is to be understood that the present disclosure has been made only by way of' example and that numerous changes in the details of construction and the combination and arrangement of parts may be resorted towithout departing from the spirit and the scope of the invention and disclosure, 6

I claim: t

1. In an underground storage system, in combination, an underground storage'cavern; a shaft extending from the surface of the earth to a region adjacent said cavern,

the lower end of said shaft being positioned below the level of the bottom of said cavern; tunnel. means connect ing said shaft with at least the bottom. region of said cavern; a first string of tubing positioned within said shaft; a second string of tubing positioned parallel to said first string of tubing; and a rotary hydraulic motor-pump unit,

ber with said second string of tubing, a fluid outlet means in said upper closure member communicating said upper chamber with said first string of tubing, means extending through said cross member for connecting said upper and lower chambers, said means being offset peripherally from said fluid inlet means, a fluid inlet means in said lower closure member, a first slotted rotor disposed eccentrically within said upper chamber, a second slotted rotor disposed eccentrically within said lower chamber, and sliding impeller vanes positioned in the slots of said first and second rotors.

2. In an underground storage system, in combination, an underground storage cavern; a shaft extending from the surface of the earth to a region adjacent said cavern, the lower end of said shaft being positioned below the level of the bottom of said cavern; tunnel means connecting said shaft with at least the bottom region of said cavern; means for sealing said shaft at a level above said tunnel means; a string of casing extending through said sealing means; a first string of tubing positioned rating said casing into an upper and a lower chamber,

a fluid inlet means in said upper closure member communicating said upper chamber with said second string of tubing, a fluid outlet means 'in said upper closure member communicating said upper chamber with said first string of tubing, means extending through said cross member for connecting said upper and lower chambers, said means being offset peripherally from said inlet means, a fluid inlet means in said lower closure member, a first slotted rotor disposed eccentrically within said upper chamber, a second slotted rotor disposed eccentri cally within said lower chamber, and expansible impeller vanes positioned in the slots of said first and second rotors; and means for introducing fluid to be stored into said cavern.

3. In an underground storage system, in combination, an underground storage cavern; a shaft extending from the surface of the earth to a region adjacent said cavern, the lower end ofsaid shaft being positioned below the level of the bottom of said cavern; tunnel means connecting said shaft with at least the bottom region of said cavern; means for sealing saidfshaft at a level above said tunnel means; a string of casing extending through said sealing means; a first string of tubing positioned within said casing; a second string of tubing mounted concentrically within said first string of tubing; a rotary hydraulic motor-pump unit comprising a cylindrical casing attached to said first string of tubing and having. an upper and lower closure member, a cross member separating said casing into an upper and a lower chamber, a fluid inlet means in said upper closure member communicating said upper chamber with said second string of tubing,

a first slotted rotor disposed eccentrically within saidv upper chamber, a second slotted rotor disposed eccentrioa'lly within saidlower chamber, and expansible impeller vanes positioned in the slots of said first and second rotors; a discharge conduit communicating with the upper end of said first string of tubing; means connected to saidsecond string of tubing for supplying power fluid to said=motor-pump unit; and means for introducing fluid-to be storedinto said cavern.

4. The underground storage system of claim 3 wherein means are provided for furnishing a part of the dis charged fluid to said means for supplying power fluid to said motor-pump unit.

5. In anwunderground storage system, in combination, an. undergroundistorage cavern; a shaft extending from the surface of the earth and communicating with said cavern; means for sealing said shaft; a string of casing extending through said sealing means, a first string of tubing mounted'concentrically within said casing; asecond string of tubing positioned parallel to said first string of tubing; means for introducing fluid to be stored into said-cavern; means for. withdrawing fluid from the bottom of said shaft comprising a rotary hydraulic motorpump unit, said unit being carriedby said'first string of tubing and connected to said second string for supply of power fluid; and a normally closed valve means at-' tached to the lower end of said casing and adapted to open upon'contact with said motor-pump unit;

6. In anunderground storage system, in combination, an underground storage cavern; a shaft extending from the surface of the earth to a region adjacent-said cavern,

the lower'end of said shaft being positioned below the level of thebottom of said cavern; tunnel means-connecting said shaftwith atleast the bottom region' of said cavern; means for sealing said shaft at a level above said tunnel means;.a string of casing extending through said sealing means, a first string of tubing mounted concentrically within said casing; a second string of tubing mounted concentrically within said firststring of tubing; means for introducing fluidto be stored into said cavern; means for withdrawing fluid from the bottom of said shaft comprising a rotary hydraulic motor-pump unit, said unitbeing carried by said first string of tubing and connected to said second string for supply of power fluid; and a normally closed valve attached to the lower" end of said string of casing, said valve being adapted to-open upon contact withsaidmotor-pump unit.-

7. In anundergroundstorage system, incombination, an underground storage cavern; an enlarged vertical shaft extending from thesurface of the earth to a region adjacent saidcavern, a tunnelconnecting said'shaft with at least the bottom region of said cavern; means for sealing'said shaft at a level above said tunnelj a string of easing extending through' said latter means'to' a position below theleveLofthe bottom region of said cavern; a firstustrin'g of tubing mounted concentrically within said casing; a second stringof tubing mounted concentrically within said first string of tubing; a rotary hydraulic motor-pump unit comprising a cylindrical casing separated by a cross member into an upper and lower chamber, a first adapter threaded into the lower end-of said first string of tubing andinto the topof'said casing, afluid inlet passageway extending l throughsaid first"-adapter communicating said upper chamber with said-second string of tubing, afluid outlet passagewayextending through said first adapter communicating said uppercharnber with said first stringiof tubing, a: passagewaythrough said cross,

member connecting said upp'erand'loWe'r chamber, said to said' first rotor; and"sl'idin"g' impeller vanes riding in the-slots of said first and second rotors; a dischar'geco'n duit communicating with the upper end of said first string of tubing; means connected to said second string of tubing for supplying power fluid to said'motor-pump unit; and means for introducing fluid to be stored" into said cavern.

8. The underground storage system of claim 7 wherein means are provided for furnishing a partof the discharged fluid to said means for supplying power fluid to saidmotor-pump unit.

9. In an underground storage system, in combination, an underground storage cavern; an enlarged vertical shaft extending from the surface of the earth toa region adjacent said cavern; a tunnel connecting said shaft with at least the bottom region of said cavern;- means for sealing said shaft above the level ofsaid tunnel, said sealing meansincluding a tubular liner at'the' top of said shaft and a well head closing the upper end of said liner; a first valve disposed above-saidwell head; a casing head above said first valve;-a string of casing extending from said casing head through said first valve, said well head, and said shaft to a position below the level of the bottom region of saidcavern; afirst string of tubing mounted concentrically within said casing; a second valve above said casing head; means for supporting the upper end of said first stringof tubing abovesaid second valve; a second stringof tubing mounted concentrically within said first string of tubing; a rotary hydraulic motor pump unit comprising a cylindricalcasing separated by a cross member into an-upper and a lower chamber, a first adapter threaded into the top of said casing and into the lower endof said first-string of tubing, a fluid inlet passageway extending; through said first adapter and communicating said upper chamber with said second string of tubing, a'fluid outlet pas sageway. extending through said-first adapter and com municating said upper chamber with said first string of tubing, a passageway through said cross member con necting said upper and lower chambers, said passageway. being substantially directly beneath said fluid out-- let passageway, a second adapter threaded-into the bottom of said casing and having-a fluid inlet passageway therethrough communicatingwith said lower chamber, a first slotted rotor disposed eccentrically within said upper chamber; a second slotted rotor disposed eccen-j trically within said lower chamber and operatively con-1 nected to said first rotor, and impeller'vanes positioned" in the slotstofsaid first andsecondrotors and'm'ain tained by'compression elements in contact with the walls of said'upper and lowerchambers; a discharge conduit communicating with the upper end of said' -first string of" tubing; means connected to said second string oftubing': for supplying power fluid to said motor-"pump unit; a normally closed valve attached to' the lower end'of" said string of: casing,said valve" being adapted to open upon lowering of said motor-pumpunit; and means for introducingfluid to be stored into said-cavern:

10. The underground storage system of claim 9 where in means are providedrfor furnishinga'part of the dis charged'fiuid to said means for supplyingpower fluid to said motor-pump unit; 1

11. In an" undergrou'ndstorage system; in combination, an underground storage cavern; an-enlarged-ver tical shaft extending from th'esurface of-the earthtoa region adjacent'said cavern;-a-tunnel connecting-said shaft with atleast the bottom region of sai'd cavern; means for sealin g tsaid shaft above thie -level of 5 saidfltum nel, said sealing-means including a tubular liner atthe'- top of said shaft and a wellhead closing the" upperen'df of said liner; a first valvedispo'sed' aboves'aidwell head; a casing head above said first valve; a string? of casingextendingifronrsaidcasing head-through said first valve; said well-1 head, and 'saida shaft t0 aaposition'ibe ,low. the level of the; bottom region of said, cavern; a

first string of tubing mounted concentrically within said 9 casing; a second valve above said casing head; means for supporting the upper end of said first string of tubing above said second valve; a second string of tubing mounted concentrically within said first string of tub ing; a rotary hydraulic motor pump unit comprising a cylindrical casing separated by a cross member into an upper and a lower chamber, a first adapter threaded into the top of said casing and into the lower end of said first string of tubing, a fluid inlet passageway extending through said first adapter and communicating said upper chamber with said second string of tubing, a fluid outlet passageway extending through said first adapter and communicating said upper chamber with said first string of tubing, the downstream end of said inlet passageway and the upstream end of said outlet passageway being disposed substantially diametrically opposite one another and adjacent to the periphery of said upper chamber, a passageway through said cross member connecting said upper and lower chambers, said passageway being substantially directly beneath said downstream end of said outlet passageway, a second adapter threaded into the bottom of said casing, a fluid inlet passageway extending through said second adapter, the upstream end of said passageway being substantially directly beneath said downstream end of said inlet passageway of said first adapter, a first slotted rotor disposed eccentrically within said upper chamber, a second slotted rotor disposed eccentrically within said lower chamber and operatively connected to said first rotor and impeller vanes positioned in the slots of said first and second rotors and maintained in contact with the walls of said upper and lower chambers by compression elements disposed in said slots between said vanes and said rotors; a discharge conduit communicating with the upper end of said first string of tubing; means connected to said second string of tubing for supplying power fluid to said motor-pump unit; a normally closed valve attached to the lower end of said string of casing, said valve being adapted to open upon lowering of said motor-pump unit; a strainer attached to and extending downwardly from said second adapter; and means for introducing fluid to be stored into said cavern.

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